1. Field of the Invention
The present invention relates to a fixing belt used in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus and an image heating and fixing apparatus for heating and fixing an unfixed image formed and carried to a recording medium.
2. Description of the Related Art
For an image forming apparatus, a fixing apparatus generally used a heat roller method in which a means for an image forming process such as an electrophotographic process, an electrostatic recording process, an electromagnetic recording process, etc. heats and fixes an unfixed image (toner image) of image information, which is to be formed and carried, to a recording medium (transfer sheet, electro fax sheet, electrostatic record, OHP sheet, printing paper, format sheet, and so on) by a transferring or direct method. This usually uses a heat source such as a halogen heater in a roller.
On the other hand, as a heating method, there is proposed and broadly used a method of heating a resin belt or metal belt needing a small amount of thermal capacity by a ceramic heater as heat source. That is, the heating method forms a nip part by interposing a heatproof belt (fixing belt) between a pressing roller as a pressing member and a ceramic heater as a heating member, introduces a recording medium, to which an unfixed toner image to be image-fixed, between the fixing belt and the pressing roller at the nip portion and carries it together with the belt so that the nip part endows the heat from the ceramic heater through the belt to the recording medium, and then fixes by heat and pressure the unfixed toner image to the surface of the recording medium by the heat and pressure of the nip part.
The fixing apparatus using the belt-heating method may constitute an on-demand type apparatus by using a member with a low amount of thermal capacity as the belt. That is, if supplying power to the ceramic heater as a heat source to generate heat to a predetermined fixing temperature only when the image forming apparatus forms the image, the apparatus has the advantages that the image forming apparatus requires short waiting time from being turned on to possibly executing the image forming (quick start ability), and the power consumption in a stand-by state is dramatically reduced (economic power consumption).
The belt heating method uses a heatproof resin as the belt, preferably a polyimide resin with a good strength and heat resistance. However, in a high-speed and high-durable machine, such resin film is not: sufficient in strength. According to that, it has been proposed to use a belt which has a substrate (base layer) made of a metal with a good strength such as SUS, nickel, aluminum, copper, etc.
In addition, Japanese Patent Application Laid-Open No. 7-114276 discloses an inducing heating method, which uses a metal belt so that it may self-heat by eddy currents caused by the electromagnetic inducement. That is, proposed is a heating apparatus to generate the eddy currents on a belt itself or a conductive member closed to the belt by the magnetic flux and generating the heat by the Joule heat. This electromagnetic inducing heating method may approach the heating area nearer to the heated member, so enhancing the efficiency of energy consumption.
To drive the fixing belt of the belt heating-type fixing apparatus, there are used a method of making a film, compressed between a pressing roller and a film guide guiding the inner surface of the belt, be driven to rotate by rotation of the pressing roller (a pressing roller driving method), and a method of, on the contrary, making the pressing roller be driven to rotate by driving an endless belt, hung down by the driving roller and a tension roller.
As examples of the fixing belt using the metal belt, Japanese Patent Application Laid-Open No. 7-13448 discloses a nickel fixing belt with a surface roughness of less than 0.5 xcexcm and a thickness of about 40 xcexcm, and Japanese Patent Application Laid-Open No. 6-222695 discloses a nickel fixing belt with a thickness of 10 to 35 xcexcm, which has a release coating layer on its outer circumference and a resin layer on its inner circumference.
The nickel endless belt may be easily produced by the nickel electroforming process. Conventionally, the nickel electroforming process was used for the improvement of abrasion resistance and the brilliance for decoration, so the obtained electroformed nickel commonly contains a large amount of sulfur. In case of using the nickel electroforming to the fixing belt, it may cause a problem in durability due to the brittle at a high temperature by the effect of the sulfur.
On the other hand, Japanese Patent Application Laid-Open No. 10-48976 discloses a fixing belt having a nickel metallic layer containing not more than 0.04% by weight of sulfur and not less than 0.2% of manganese. And, in Japanese Patent No. 2706432, proposed is a fixing belt having an endless electroformed sheet with a microvickers hardness of 450 to 650, which is made of nickel-manganese alloy containing 0.05 to 0.6% by weight of manganese.
However, in case of the belt heating method, particularly using the metal belt, the heat resistance and durability are still concerned because the belt itself is carried by the rotation and repeatedly belt bending at the nip part and its gate, which easily cause mechanical fatigue.
An object of the present invention is to provide a high-durable fixing belt and an image heating apparatus with high durability and high reliability for using a heating member needing a small amount of thermal capacity to enable heating with low energy.
The fixing belt according to the present invention includes at least a release layer and a metal layer made by electroforming nickel, in which the electroformed nickel has a crystal orientation ratio I(200)/I(111) of 3 or more, in which a surface(200) is preferentially grown, and a microvickers hardness of 280 to 450.
The fixing belt according to the present invention uses a nickel-electroformed metal layer with a good strength as a base layer, in which a crystal orientation ratio I(200)/I(111) of the electroformed nickel is not less than 3 and a microvickers hardness is ranged in 280 to 450, whereby the fixing belt may show high durability at, particularly, high temperature. And, by using such fixing belt, an image heating apparatus with high durability and high reliability may be provided.